Post updated: March 19, 2025

Hilo has a way of weaving magic into its landscape. With its emerald rainforests, thundering waterfalls, and mist-laden valleys, this sleepy town on the Big Island feels like a place where legends still roam. At the heart of this mysticism is the Wailuku River—Hawai‘i’s longest river—cascading down from an elevation of 10,800ft on eastern slope of Mauna Kea before carving its way between ancient lava flows of Mauna Kea and Mauna Loa. Most visitors stop at Rainbow Falls or Boiling Pots, two stunning but treacherous landmarks where swimming is prohibited due to being higher upstream and therefore having much stronger currents. For those willing to explore, the Wailuku River reveals hidden swimming holes, serene pockets of water where you can safely immerse yourself in its sacred embrace. While I’m not going to openly share the exact locations of these numerous swimming holes, I do want to showcase the beauty and mysticism of the Wailuku River and guide you to do so in a safe and respectful manner. 

Safety Note: The Wailuku River accounts for 25% of all river drowning in Hawaii

The Spirit of Wailuku River

The Wailuku River’s name translates to “Destructive Waters” in Hawaiian, a testament to both its beauty and its power. But beyond its physical force, the river is steeped in mythology.

One of the most famous moʻolelo (legends) tells of Kuna, a powerful moʻo (giant lizard) who guarded the river and its falls, terrorizing those who lived nearby. According to legend, the moon goddess Hina, who resided in a cave behind Rainbow Falls, endured Kuna’s relentless attacks as he sent torrents of water and boulders crashing down the river trapping her in the cave. In response, the demigod Māui, Hina’s son, came to her aid, striking Kuna with his great strength and eventually driving the beast from the river. Some say that the boiling, churning waters of Wailuku still bear the scars of this epic battle, a reminder of the river’s untamed spirit and the gods who shaped its course.

This moʻolelo is more than just a story—it is a warning. The river may appear calm, but like Kuna, it can turn violent in an instant, fed by unseen rains from the mauka (uplands). If the voice of the river changes or a sudden wind blows  downstream, take heed—these are signs of a rain squall already raining in the mountains. The legend also teaches that caves and ledges along the river, once thought to be safe, can become traps when the waters rise. Beneath the surface, hidden  currents create a deadly swirling effect where even the strongest swimmers can be caught and tumbled endlessly. Even experienced locals have lost their lives to Wailuku’s unforgiving waters, a sobering reminder that this river demands not just admiration, but deep respect.

The River’s Power: Safety First

Before stepping foot in any freshwater pool, understanding Wailuku’s temperament is crucial. This mighty river is prone to flash flooding, with sudden surges that can turn tranquil waters into torrents. Always check the current flow rate before swimming. While flash flooding is less common in the summer when rainfall is lower, tropical storms can still bring unexpected and extreme deluges. One of the most dramatic examples was The Millennium Flood in November 2000, when two stacked tropical storms unleashed record-breaking rainfall—27.2 inches (690 mm) in just 24 hours—on Hilo, devastating the region. More recently, on August 23, 2018, Hurricane Lane dumped nearly three feet of precipitation on Hilo, causing widespread flooding. Even when skies are clear, conditions can change rapidly, making it critical to check river flow rates before swimming.

Additionally, crystal-clear water is essential. Murky or stagnant water can carry leptospirosis, a bacterial infection that thrives in freshwater. If the water isn’t visibly clean, don’t take the risk. And it is always best to choose a hot and sunny day. The sun is much preferred to warm you on a hot black volcanic boulder after a cold dip. Water temperatures hover around 70–75°F (21–24°C)—refreshing, but chilling if you’re not prepared. 

Know Your Depths Before You Dive

Speaking of boulders, Wailuku swimming holes often have underwater hard to see rocks and submerged ledges, making depth unpredictable. The golden rule? Always check before you jump. Even if you see others taking the plunge, water levels can change with rainfall upstream. What was deep yesterday might be dangerously shallow today. I’ve personally went to jump in butt first on what seemed like a perfect summer day, only to smash my tailbone on an unseen rock. It can happen to anybody and should not be disregarded. 

Respect the Land, Respect the Culture

Hawaiians have a deep reverence for their land, and that respect extends to every forest, valley, and stream. If you find one of Wailuku’s hidden swimming holes, treat it as a privilege, not a playground. Keep noise levels low by not blaring loud music, as many of these places hold cultural and spiritual significance. Do not leave trash behind. Better yet, bring a garbage bag and if you see litter, pick it up. Some areas near the riverbanks are home to large homeless encampments, and while it may seem like trash is scattered, that doesn’t make it okay to add to the problem. Be a good steward and leave the area better than you found it. If locals see you pick up rubbish, they will respect you and welcome you, which in Hawaii is the highest compliment. 

The Search for Serenity

Finding a quiet swimming hole to yourself along the Wailuku River is a reward for those who tread carefully and respectfully. It’s a place to feel connected to nature, to the island’s history, and to something beyond the tangible. When you slip into the cool, clear water, surrounded by towering ferns and the distant rush of waterfalls, you’ll understand why this river has inspired myths for centuries. But above all, remember: Wailuku is not just a destination, it is a living force, one that demands both awe and respect.